A fine line between species and ecotype: a case study of Anoplistes halodendri and A. kozlovi (Coleoptera: Cerambycidae) occurring sympatrically in Mongolia

Abstract

This paper discusses ecological adaptation based on a case study of Anoplistes halodendri and Anoplistes kozlovi (Coleoptera: Cerambycidae) that occur in the arid zone of Mongolia. By applying an integrative taxonomy approach, we revealed one of the first documented cases of sympatrically occurring ecotypes in Polyphaga and the second case of ecotypes in the family Cerambycidae. The results of the analysis of the ecological data, molecular analysis of mitochondrial (COI) and nuclear (ArgK and CAD) genes, as well as a detailed morphological examination, which consisted of a study on the male genitalia including the endophallic structures, supported the hypothesis that these two entities, which are commonly considered separate species, represent only ecologically adapted forms that are associated with rocky hills and sandy/gravelly plains, respectively. Therefore, a synonym is restored: Anoplistes halodendri minutus Hammarström, 1892 = Asias kozlovi Semenov and Znojko, 1934, syn. res. The differences in the elytral pattern and shade appear to be adapted to the different substrates in these distinct habitats. A probable scenario assumes that these two forms arose in parapatry, independently in multiple populations, under parallel speciation during the intensification of the aridification across the region in the period during which the Gobi Desert was formed (~ 24 to 2.6 Ma) and they may evolve into separate species in the future. The phylogenetic relationships of some taxa representing the most closely related genera of the tribe Trachyderini were analysed and the questioned species status of Anoplistes jacobsoni was confirmed. Low interspecific differences in the endophallic structures in the genus Anoplistes and between some species of the genus Amarysius indicate that they are evolutionarily relatively young groups. The practical differences between ecotype and subspecies are also discussed.